Add Claude Sonnet 4.6 Thinking model support

[sk0x0y]

Problem

Google Antigravity now supports Claude Sonnet 4.6 (thinking) as a reasoning model (see official docs), but this model is not defined in the default opencode.json configuration.

Current state:

• antigravity-claude-sonnet-4-6: Defined ✓ (no thinking support)
• antigravity-claude-sonnet-4-6-thinking: Missing ❌
• antigravity-claude-opus-4-6-thinking: Defined ✓

Evidence

From Antigravity Models Documentation:

For the core reasoning model, Antigravity offers leading frontier models from the Google Vertex Model Garden:

• GPT-OSS-120b
• Claude Opus 4.6 (thinking)
• Claude Sonnet 4.6 (thinking) ← Available but not configured
• Gemini 3 Flash
• Gemini 3.1 Pro (low)
• Gemini 3.1 Pro (high)

Proposed Solution

Add antigravity-claude-sonnet-4-6-thinking model definition with thinkingConfig variants (matching existing Opus 4.6 Thinking pattern):

"antigravity-claude-sonnet-4-6-thinking": {
  "name": "Claude Sonnet 4.6 Thinking (Antigravity)",
  "limit": {
    "context": 200000,
    "output": 64000
  },
  "modalities": {
    "input": ["text", "image", "pdf"],
    "output": ["text"]
  },
  "variants": {
    "low": {
      "thinkingConfig": {
        "thinkingBudget": 8192
      }
    },
    "max": {
      "thinkingConfig": {
        "thinkingBudget": 32768
      }
    }
  }
}

Variant Options

Following the existing antigravity-claude-opus-4-6-thinking pattern:

• No variant (dynamic): Model decides thinking budget automatically
• low: thinkingBudget: 8192
• max: thinkingBudget: 32768

Use Case

This would enable users to configure categories like unspecified-low with thinking capabilities:

"unspecified-low": {
  "model": "google/antigravity-claude-sonnet-4-6-thinking",
  "variant": "low"
}

Related

• Anthropic's Claude Sonnet 4.6 announcement confirms extended thinking support
• Sonnet 4.6 uses "adaptive thinking" with effort settings

[github-actions]

👋 Thanks for opening this issue!

Not a runtime bug; default model presets are missing this entry. You can use it now by adding a custom model in ~/.config/opencode/opencode.json (or via opencode auth login -> Configure models) with model: "claude-sonnet-4-6-thinking" and your desired thinkingConfig variants.

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